The present invention relates to a closed circuit blade cooled turbine for improving the performance of gas turbine equipment by supplying a refrigerant inside the moving blades of a turbine, circulating and collecting it.
A conventional turbine moving blade cooling system is generally a closed circuit blade cooling system for warming or cooling a wheel which is a holding member of the moving blades first by introducing air extracted from an optional stage of a multistage compressor to a rotor which is a multistage turbine group, moderates the temperature gradient generated in the wheel, and then cooling and lowering the moving blade metal temperature by supplying and circulating air inside the moving blades, and discharging air after cooling into the gas flow path of the turbine as it is.
However, recently in gas turbine equipment, for the purpose of energy conservation and environmental maintenance, realization of high efficiency of a system has been required. As a means of realization of high efficiency, a closed circuit blade cooling system is used, which system has a constitution that a cooling medium (hereinafter referred to as a refrigerant) after cooling of the moving blades is all collected without discharging it into the turbine gas flow path as exhaust gas as it is and returned between the compressor and the combustor via the return line.
Thereby, not only the loss extracted from the compressor as a refrigerant is recirculated and made up but also the thermal energy received by turbine cooling is added to gas before combustion and hence a constitution that high efficiency improvement is available is realized.
Such a closed circuit blade cooling system or turbine is described in, for example, Japanese Patent Application Laid-Open 7-189740 and Japanese Patent Application Laid-Open 9-242563.
Meanwhile, in the closed circuit blade cooling turbine, a refrigerant to be supplied from the still side is generally supplied to the rotor via a single supply path without distinction of a refrigerant for the first stage moving blades (moving blades positioned on the uppermost stream side of main gas of the gas turbine) and a refrigerant for the second stage moving blades (moving blades positioned on the downstream side of the first stage moving blades) and also when the refrigerant is to be collected on the still side from the rotor after cooling each moving blade, it is collected via a single collection path without distinction of the refrigerant for the first stage moving blades and the refrigerant for the second stage moving blades. Therefore, the branch point of a refrigerant to be supplied to the first stage moving blades and the second stage moving blades and the junction of a refrigerant to be collected from the first stage moving blades and the second stage moving blades are located inside the rotor. Between the branch point and the junction in the rotor, a refrigerant supply flow path and a refrigerant collection flow path for the first stage moving blades and a refrigerant supply flow path and a refrigerant collection flow path for the second stage moving blades are installed and these flow paths have a plurality of parallel flow paths for refrigerant supply and a plurality of parallel flow paths for refrigerant collection which are connected to the respective refrigerant paths in the moving blades at each stage.
However, there are the following problems imposed in a conventional closed circuit blade cooling turbine.
Since main gas passing through the second stage moving blades does its work in the first stage moving blades, the temperature of main gas in the second stage moving blades is lower than that of the first stage moving blades. When the temperature of main gas at the outlet of the combustor is on the level of 1500° C., the difference in the temperature of main gas between the first stage moving blades and the second stage moving blades is more than 200° C. Even if the allowable metal temperature of the first stage moving blades is made higher than that of the second stage moving blades depending on the material characteristics such as the material kind, single crystal, polycrystal, and others, it is impossible to compensate for more than 200° C. of difference in the temperature of main gas by the material and hence it is necessary that the first stage moving blades supply and cool a refrigerant at a flow rate higher than that of the second stage moving blades.
Inside the rotor, as mentioned above, the refrigerant flow path (refrigerant supply flow path and refrigerant collection flow path) for the first stage moving blades and the refrigerant flow path (refrigerant supply flow path and refrigerant collection flow path) for the second stage moving blades are installed. In this case, assuming that the flow resistance of the refrigerant flow path for the first stage moving blades and the flow resistance of the refrigerant flow path for the second stage moving blades in the moving blades and rotor are equal to each other, a refrigerant in the same amount flows through the first stage moving blades and second stage moving blades respectively.
However, by doing this, as mentioned above, an appropriate refrigerant flow rate cannot be distributed in the first stage moving blades and second stage moving blades which are different in the necessary refrigerant flow rate. Namely, if a necessary amount of refrigerant is supplied to the first stage moving blades, an excessive amount of refrigerant flows through the second stage moving blades and the thermal effect of the turbine is reduced. Inversely, if a necessary amount of refrigerant is supplied to the second stage moving blades, the refrigerant of the first stage moving blades is insufficient and the first stage moving blades exceed the allowable metal temperature.
On the basis of the aforementioned respects, even if the sectional area and resistance of the refrigerant supply flow path in each of the rotor and moving blades are estimated at the design stage and each refrigerant flow path is designed and manufactured on the basis of it so that an appropriate flow rate flows in the moving blades at each stage, actually variations are easily caused to each product and after assembly and manufacture, when the metal temperature of each of the first stage moving blades and second stage moving blades is deviated from the design value, it is necessary to adjust the flow rate distribution of a refrigerant to be supplied depending on the metal temperature of each of the first stage moving blades and second stage moving blades.
A refrigerant supplied to the rotor via the single supply path is branched to a refrigerant for the first stage moving blades and a refrigerant for the second stage moving blades in the rotor and the refrigerants after cooling the first stage moving blades and second stage moving blades join in the rotor and are collected outside the rotor via the single collection path. Therefore, it is necessary to adjust the refrigerant flow rate of each of the first stage moving blades and second stage moving blades and in this case, it is necessary to consider at what position of the refrigerant flow path the flow path resistance for flow rate adjustment is to be set.
In the general constitution of the rotor that the rotor is locked with bolts with a plurality of wheels and spacers overlapped in the axial direction, when a flow path resistor is installed inside the rotor, whenever the flow rate for the moving blades at each stage is to be adjusted, it is necessary to remove the locking bolts of the rotor and break down it and hence the operation is complicated extremely and the operation time and cost are increased. Therefore, it is a problem how to adjust the flow rate simply without breaking down the rotor.